|Astrophysical parameters of Galactic open clusters|
We present a catalogue of astrophysical data for 520 Galactic openclusters. These are the clusters for which at least three most probablemembers (18 on average) could be identified in the ASCC-2.5, a catalogueof stars based on the Tycho-2 observations from the Hipparcos mission.We applied homogeneous methods and algorithms to determine angular sizesof cluster cores and coronae, heliocentric distances, mean propermotions, mean radial velocities, and ages. For the first time we derivedistances for 200 clusters, radial velocities for 94 clusters, and agesof 196 clusters. This homogeneous new parameter set is compared withearlier determinations, where we find, in particular, that the angularsizes were systematically underestimated in the literature.
|Comparison of the Luminosity Functions of Open Clusters Based on USNO-A1 Data|
The luminosity and mass functions of a group of Galactic open clustersare constructed by applying a statistical method to photometric datafrom the USNO-A1 catalog. Despite some limitations, this catalog can beused for statistical analyses in Galactic astronomy. Pairwisecomparisons of the derived cluster luminosity functions are performedfor five age intervals. The differences between the luminosity functionsof the open clusters are not statistically significant in most cases. Itis concluded that the luminosity functions are approximately universalthroughout a large volume in the solar neighborhood. Combined luminosityand mass functions are constructed for six age intervals. The slope ofthe mass spectrum may vary somewhat from cluster to cluster, and themean slope may be somewhat higher than the Salpetervalue.
|Proper Motions of Open Star Clusters and the Rotation Rate of the Galaxy|
The mean proper motions of 167 Galactic open clusters withradial-velocity measurements are computed from the data of the Tycho-2catalog using kinematic and photometric cluster membership criteria. Theresulting catalog is compared to the results of other studies. The newproper motions are used to infer the Galactic rotation rate at the solarcircle, which is found to be ω0=+24.6±0.8 km s-1 kpc-1.Analysis of the dependence of the dispersion of ω0 estimates onheliocentric velocity showed that even the proper motions of clusterswith distances r>3 kpc contain enough useful information to be usedin kinematic studies demonstrating that the determination of propermotions is quite justified even for very distant clusters.
|The Distance Scale for Classical Cepheid Variables|
New radii, derived from a modified version of the Baade-Wesselink (BW)method that is tied to published KHG narrowband spectrophotometry, arepresented for 13 bright Cepheids. The data yield a best-fittingperiod-radius relation given bylog=1.071(+/-0.025)+0.747(+/-0.028)logP0. In combination with other high-quality radiusestimates recently published by Laney & Stobie, the new data yield aperiod-radius relation described bylog=1.064(+/-0.0006)+0.750(+/-0.006)logP0, which simplifies to ~P3/4.The relationship is used to test the scale of Cepheid luminositiesinferred from cluster zero-age main-sequence (ZAMS) fitting, for whichwe present an updated list of calibrating Cepheids located in stellargroups. The cluster ZAMS-fitting distance scale tied to a Pleiadesdistance modulus of 5.56 is found to agree closely with the distancescale defined by Hipparcos parallaxes of cluster Cepheids and alsoyields Cepheid luminosities that are a good match to those inferred fromthe period-radius relation. The mean difference between absolute visualmagnitudes based on cluster ZAMS fitting,C, and those inferred for 23 clusterCepheids from radius and effective temperature estimates,BW, in the sense of C-BW is+0.019+/-0.029 s.e. There is no evidence to indicate the need for amajor revision to the Cepheid cluster distance scale. The absolutemagnitude differences are examined using available [Fe/H] data for thecluster Cepheid sample to test the metallicity dependence of theperiod-luminosity relation. Large scatter and a small range ofmetallicities hinder a reliable estimate of the exact relationship,although the data are fairly consistent with predictions from stellarevolutionary models. The derived dependence isΔMV(C-BW)=+0.06(+/-0.03)-0.43(+/-0.54)[ Fe/H].
|A study of spatial structure of galactic open star clusters|
In order to study the relation between the core and corona in galacticstar clusters, the spatial structure of 38 rich open star clusters hasbeen studied using radial density profiles derived from the photometricdata of the Digital Sky Survey. The shape of the radial density profileindicates that the corona, most probably, is the outer region around thecluster. It can exist from the very beginning of the cluster formationand dynamical evolution is not the reason for its occurrence. The studydoes not find any relation between cluster size and age but indicatesthat the clusters with galacto-centric distances >9.5 kpc have largersizes. Further, we find that the average value of the core radius is1.3+/- 0.7 pc and that of annular width of the corona is 5.6+/- 1.9 pc,while average values of densities of cluster members in the core andcorona are 15.4+/- 9.9 star/pc2 and 1.6+/- 0.99star/pc2 respectively. Average field star contaminations inthe core and corona are ~ 35% and 80% respectively. In spite of smallerdensities in the coronal region, it contains ~ 75% of the clustermembers due to its larger area in comparison to the core region. Thisclearly demonstrates the importance of the coronal region in studiesdealing with the entire stellar contents of open star clusters as wellas their dynamical evolution. In contrast to the cluster cores, thestructure of coronal regions differs significantly from one cluster toother.
|The distribution of bright OB stars in the Canis Major-Puppis-Vela region of the Milky Way|
The picture of the young stellar groups in the Canis Major-Puppis-Vela(215 deg
|Absolute proper motions of 181 young open clusters.|
|Catalogue of blue stragglers in open clusters.|
An extensive survey of blue straggler candidates in galactic openclusters of both hemispheres is presented. The blue stragglers wereselected considering their positions in the cluster colour-magnitudediagrams.They were categorized according to the accuracy of thephotometric measurements and membership probabilities. An amount of 959blue straggler candidates in 390 open clusters of all ages wereidentified and classified. A set of basic data is given for everycluster and blue straggler. The information is arranged in the form of acatalogue. Blue stragglers are found in clusters of all ages. Thepercentage of clusters with blue stragglers generally grows with age andrichness of the clusters. The mean ratio of the number of bluestragglers to the number of cluster main sequence stars is approximatelyconstant up to a cluster age of about 10^8.6^ yr and rises for olderclusters. In general, the blue stragglers show a remarkable degree ofcentral concentration.
|Integrated photometric properties of open clusters|
Galactic open clusters provide an abundant sample of stellar aggregatesof various sizes, ages and metal abundances, apt to constitute atemplate for comparison with star systems in other galaxies. In thispaper we present and discuss a standard methodology to synthesize U,B,Vfluxes and colours, and apply it to a set of 138 open clusters. Resultsare compared with previous ones available in the literature. We wereable to calibrate a mass-luminosity relation by which we evaluated themass of ~400 open clusters, leading to a well defined present-day massfunction. The number-complete sample of galactic open clusters presentedin Battinelli & Capuzzo-Dolcetta (1991) is enlarged of a 15%.
|Formation and evolutionary properties of the Galactic open cluster system|
Results are reported from a statistical analysis of observational dataon 100 open clusters within 2 kpc of the sun, selected from the catalogof Lynga (1987). The selection criteria and the completeness of thesample are discussed; the data are compiled in a table; and the analysisresults are presented in a series of graphs and characterized in detail.A cluster formation rate of 0.45 clusters/kpc Myr is found,significantly lower than the rates determined previously (using clusterswithin 1 kpc of the sun) and corresponding to a cluster star-formationefficiency of 0.0063. The low average cluster lifetime (about 10 Myr)suggests that clusters are formed as unstable systems.
|Component Analysis of Open Clusters|
|Young stellar-gas complexes in the Galaxy|
It is found that about 90 percent of OB-associations and o-b2 clusterssituated within 3 kpc of the sun can be united into complexes withdiameters of 150-700 pc. Almost all of these clusters contain giantmolecular clouds with a mass greater than about 100,000 solar masses. Anumber of complexes are associated with giant H I clouds; a few of thesmall complexes are situated in the HI caverns. The concentration ofOB-associations and young clusters in star complexes attests to theircommon origin in the supergiant gaseous clouds.
|Catalog of open clusters and associated interstellar matter.|
|The peculiar planetary nebula NGC 2346 and its nucleus|
The V light curve of the NGC 2346 nucleus (V 651 Mon) from 1981 to 1986is constructed on the basis of published data and observations obtainedwith the 67-cm Schmidt and 182-cm Ekar telescopes at Asiago Observatory.This curve shows the star to be an A5-V single-line spectroscopic binarywith deep eclipselike minima and a photometric period of 15.995 d; in1986, however, the variation ceased and the star became constant, as ithad been prior to 1981. The apparent eclipses are attributed to the slowpassage in front of the system of a dark gas/dust cloud ejected by thehot collapsed companion. Also presented are spectra and images of the PNand its nucleus obtained at Asiago and ESO: little change is seen in thespectra during the eclipselike episode, and the images reveal anextended nebula with clear bipolar structure and a central35-arcsec-diameter zone of uneven density.
|Catalogue of UBV Photometry and MK Spectral Types in Open Clusters (Third Edition)|
|Investigation of the initial mass spectrum of open star clusters|
The mass spectra of 228 open star clusters were derived by comparison ofcolor-magnitude diagrams with evolutionary tracks. The application tobinary stars showed the reliability of the mass determination. Thederived mass spectra were fitted by power laws as well as exponentiallaws. It could be shown that both approximate the mass spectra of openstar clusters on the same average significance level. The presentinvestigation revealed a correlation of the slope of the mass spectrawith the cluster age, whereas a detected correlation of the slope withgalactocentric distance is slight. The results suggest that the slope ofthe mass spectrum increases with increasing cluster and galactocentricdistance. These findings are discussed with respect to their reasons andprevious results concerning open clusters and field stars.
|Catalogue of Eclipsing and Spectroscopic Binary Stars in the Regions of Open Clusters|
|Integrated Photometric Parameters of Open and Globular Clusters|
|Open clusters and galactic structure|
A total of 610 references to 434 clusters are employed in thecompilation of a catalog of open clusters with color-magnitude diagramson the UBV or RGU systems. Estimates of reddening, distance modulus, ageand number of cluster members are included. Although the sample isconsidered representative of the discoverable clusters in the galaxy,the observed distribution is nonuniform because of interstellarobscuration. Cluster distribution in the galactic plane is found to bedominated by the locations of dust clouds rather than by spiralstructure. The distributions of clusters as a function of age andrichness class show that the lifetimes of poor clusters are much shorterthan rich ones, and that clusters in the outer disk survive longer thanthose in the inner disk. An outer disk age which is only about 50% theage of the globular clusters is indicated by cluster statistics. Thethickening of the galactic disk with increasing galactocentric distancemay be due to either a younger dynamical age or a lower gravitationalpotential in the outer regions.
|Three-colour photometry of a field in the galactic anticentre section near NGC 2360.|
|A catalogue of galactic clusters observed in three colours|
This catalogue contains photometric data for 190 galactic clusters, allobserved in UBV or RGU. The distances of the young clusters (with spless than b3) have been calculated or recalculated according to method Aof Becker (1963). The galactic distribution of these clusters confirmstheir role of being good spiral tracers.
|NGC 3105 - Further photoelectric UBV observations|
NGC 3105 (galactic longitude 279.92 deg, latitude +0.28 deg) isconfirmed to be a distant young cluster located 5.5 kpc from the sun onthe basis of photoelectric photometry of 34 stars. Its mean B-V colorexcess is 1.08 plus or minus 0.03 (m.e.). The earliest spectral type isB2, making NGC 3105 a useful spiral tracer. It contains six probablesupergiants: three red, one yellow, and two blue, one of the latterbeing confirmed spectroscopically. One of the red supergiants appears tobe one component of a red-blue close binary. Three Be stars are alsoprobable members.
|NGC 2345, a moderately young open cluster in Canis Major|
Abstract image available at:http://adsabs.harvard.edu/abs/1974A&AS...16...33M